Sealing and wiping means for ball screw actuator

ABSTRACT

A resiliently deformable elastomeric ring seats in a non-rotary manner in a continuous inner circumferential channel of a nut of a ball screw actuator to cooperate with the screw of the actuator as a wiper and sealing means. The channel is wider than the ring to permit slight axial shift of the ring and the ring has at least one continuous narrow outer circumferential sealing rib in contact with the bottom of the channel that yields sufficiently under radial compression to compensate for the range of clearances afforded by the given tolerances of the nut and screw to insure that the body of the ring will not be radially compressed to a destructive degree.

United States Patent Patterson [45] July 25, 1972 [54] SEALING ANDWIPING MEANS FOR 3,116,931 1/1964 Edwards ..74/4s9 x BALL SCREW ACTUATOR3,532,004 10/1970 Nilsson ..74 459 [72] Inventor: Donald S. Patterson,Corona, Calif. [73] Assignee: Sargent Industries, Inc., Los Angeles,

Calif.

[22] Filed: Sept. 21, 1970 [21] App]. No.: 74,032

[51] lnt.Cl .Fl6h 55/22,Fl6h 57/04 [58] Field of Search ..74/459, 467

[56] References Cited I UNITED STATES PATENTS 2,757,548 3/1956 Smith etal ..74/459 X Griswold ..74/459 X Primary Examiner-Leonard H. GeriinA1t0mey-Smyth, Roston & Pavitt [57] ABSTRACT A resiliently deformableelastomeric ring seats in a non-rotary manner in a continuous innercircumferential channel ofa nut of a ball screw actuator to cooperatewith the screw of the ac- 23 Claims, 11 Drawing Figures Patented July25, 1972 3,678,776

Will

.1 716. 5: firazfi o I I [VI/EN 7'01? 20d fio/wua 5. 1 /1 rrs/asmSEALING AND WIPING MEANS FOR BALL SCREW ACTUATOR BACKGROUND OF THEINVENTION In the normal functioning of a ball screw actuator suitablelubricant is employed to minimize frictional resistance to rela tiverotation between the nut and the screw of the actuator. When the screwextends axially relative to the nut, the relatively thick lubricantcoating thereon is exposed to pick up foreign particles which arecarried back into the interior of the nut when the screw is subsequentlyretracted. Repeated cycling of the screw not only progressively reducesthe amount of lubricant that is effective between the nut and the screwbut also progressively contaminates the lubricant. As a consequenceexcessive wear can be avoided only by cleaning the parts and replacingthe lubricant at relatively short intervals.

One prior art answer to this problem is to provide the nut with an innercircumferential ring that serves as a wiper to remove the foreignparticles on the screw as the screw retracts into the interior of thenut. Such a wiper ring does reduce to a useful degree the entrance offoreign particles into the interior of the nut but, nevertheless, doesnot embrace the nut with sufficient tightness to serve as a highlyefficient barrier against intrusion of the foreign particles. Therelative looseness of the ring, moreover, permits escape of lubricantfrom the interior of the nut and therefore does not prevent theeffective portion of the lubricant from being progressively diminishedat an undesirable rate. Thus although such a wiper ring does reduce wearand does prolong the intervals during which the ball screw actuator mayoperate without being serviced, there is a need for a tighter fittingwiper ring that will not only block the entrance of foreign particlesbut will also serve as a seal against the loss of lubricant.

The underlying reason for the relatively loose fit of the prior artwiper rings is found in the range of clearances between the nut and thecooperating screw that is afforded by the dimensional tolerances of thenut and the screw. On the one hand, the wiper ring must be of sufficientradial dimension to serve its purpose at the maximum clearance in thisrange and, on the other hand, it must be sufficiently capable of radialcontraction to function at the minimum clearance in the range. Too oftena wiper ring that is effective at the maximum clearance in the range isso tightly compressed at the other end of the range that it binds orfreezes with consequent destruction of the ring.

One way that such a structural failure has been prevented has been todesign the wiper ring with optimum dimensions for a relatively smallclearance in the range of clearances with the consequence that the ringis not efficient when the clearance is relatively large. Another waythat the difficulty has been avoided has been to make the ring largelyif not entirely of a highly yieldable fibrous material such as feltwhich may be readily compressed without excessive resistance. Suchfibrous material, however, does not provide an effective seal forcontainment of the lubricant.

The object of the present invention is to provide a wiping and sealingring that will function over the whole range of clearances for giventolerances in the dimensioning of the nut and screw of a ball screwactuator.

SUMMARY OF THE INVENTION The elastomeric ring is of appreciable lesserwidth than the channel in which the elastomeric ring seats so that theelastomeric ring is free to shift axially sufficiently to compensate forvariations in backlash between the nut and the screw and, of course, theinterlocking means is designed to permit this freedom.

The elastomeric ring has a body that provides the width dimension of thering and the ring is further formed with at least one continuous outercircumferential sealing rib or lip of substantially less width than thebody, the rib or lip maintaining sealing contact with the cylindricalbottom surface of the inner circumferential channel in which theelastomeric ring is seated. The radial dimension of the elastomeric ringincluding its outer circumferential sealing rib relative to the radialdimension of the channel is of a magnitude for the ring to form aneffective seal between the nut and screw without binding compression ofthe body of the ring at the minimum clearance within the range ofclearances that is provided by the given tolerance in the dimensioningof the nut and the given tolerance in the dimensioning of the screw.

At the minimum clearance in the range of clearances the relativelynarrow sealing rib is greatly compressed but the body of the elastomericring as distinguished from the sealing rib is not compressed to suchdegree as to cause the elastomeric ring to freeze or to be unduly heatedby friction. Thus compensation for the whole range of clearances betweenthe nut and screw is provided primarily by resilient compression of thesealing rib as distinguished from compression of the body of the ring.

In one practice of the invention the elastomeric ring has two continuouscircumferential sealing ribs which lie on opposite sides of the meansthat interlocks the elastomeric ring with the nut. In an alternatepractice of the invention two sealing ribs lie on opposite sides of theinterlocking means in the immediate vicinity of the interlocking meansbut the two ribs merge into one central rib that extends over theremainder of the outer circumference of the elastomeric ring.

The features and advantages of the invention may be understood from thefollowing detailed description and the ac companying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to beregarded as merely illustrative:

FIG. 1 is a sectional view of a selected embodiment of the elastomericring;

FIG. 2 is a fragmentary plan view of the ring as seen along the line 2-2of FIG. 1;

FIG. 3 is a fragmentary sectional view showing the elastomeric ringmounted in a nut of a ball screw actuator;

FIG. 4 is a fragmentary sectional view of a second embodiment of theelastomeric ring;

FIG. 5 is a fragmentary sectional view showing howa key may be employedto interlock an elastomeric ring with the surrounding nut;

FIG. 6 is a fragmentary sectional view illustrating another manner inwhich an elastomeric ring may be interlocked with a surrounding nut;

FIG. 7 is a fragmentary sectional view as seen along the line 7-7 ofFIG. 6;

FIG. 8 is a fragmentary plan view of another embodiment of theelastomeric sealing ring;

FIG. 9 is a transverse sectional view of the sealing ring as seen alongthe line 9-9 of FIG. 8;

FIG. 10 is a fragmentary sectional view along the line 10- 10 of FIG. 8showing how the elastomeric ring is interlocked with the surroundingnut; and

FIG. 11 is a view similar to FIG. 10 showing how a radial pin may beemployed to interlock the elastomeric ring with the surrounding nut.

DESCRIPTION OF THE SELECTED EMBODIMENTS OF THE INVENTION In FIGS. 1-3illustrating the first embodiment of the invention, a ring, generallydesignated 20, made of a suitable resiliently deformable elastomer isadapted to be mounted inside a nut 22 of a ball screw actuator tocooperate with a screw 24 of the actuator. For this purpose an innercircumferential channel 25 is formed in the end of the nut 22, thechannel having a cylindrical inner circumferential surface.

The resilient ring has a body 26 and is formed with at least onecontinuous outer circumferential sealing lip or rib in continuouspressure contact with the inner surface of the inner circumferentialchannel 25. In this particular embodiment of the invention the ring 20has two outer circumferential sealing ribs 28 adjacent its two oppositeside edges respectively. It is to be noted that the width of the body 26of the ring is appreciably less than the width of the inner channel togive the ring sufficient freedom to shift axially in the inner channelto accommodate variation in the backlash between the nut 22 and thescrew 24.

It is contemplated that the resilient ring 20 will be suitablyinterlocked with the nut 22 to prevent rotation of the ring relative tothe nut and various means may be employed for this purpose in variouspractices of the invention. In this first embodiment of the inventionthe interlocking relationship is accomplished by providing the resilientring 20 with a radial projection 30 that extends into a radial bore 32of the nut 22. It is important to note that the radial bore 32 issufliciently oversized relative to the radial projection 30 to permitthe desired freedom for axial shift of the resilient ring in the innerchannel 25. It is also to be noted that the relative dimensions are suchthat neither of the two sealing ribs 28 reaches the radial bore 32 ateither of the two extreme positions of the resilient ring in the innerchannel 25. Thus the radial bore 32 serves its purpose without providinga leakage path for lubricant that is confined in the nut.

In the well known manner the nut 22 has an inner thread that cooperateswith an outer thread of the screw 24 to form a helical race forantifriction balls of the actuator. Thus the nut 22 is formed with aninner circumferential helical land 34 with the turns of the landseparated by a helical groove 35. In like manner the screw 24 is formedwith an outer circumferential helical land 36 with the turns of the landseparated by a helical groove 38 that cooperates with the helical grooveof the nut to form the helical ball race.

The resilient ring 20, in effect, forms a continuation of the innercircumferential surface of the nut 22 and therefore continues the land34 and the groove 35 of the nut but the unrestrained inside diameter ofthe resilient ring is less than the inside diameter of the nut asrequired for sealing contact with the screw 24.

The width of the resilient ring 20 is defined by two parallel planesthat are normal to the axis of the ring and this width may vary invarious practices of the invention. It is preferred, however, that thewidth of the resilient ring be approximately the width of one full turnof the external screw thread of the screw 24. Thus in FIG. 1 the widthof the resilient ring 20 is the width of one full turn of an inner land40 and an adjacent inner helical rib 42 of the ring.

In accord with the usual practice the internal dimension of the nut 22is within a given tolerance and the external dimension of the screw 24is within a given tolerance and by virtue of these two tolerances thereis a given range of clearances between the nuts and the screws when thenuts and screws are mated in the random manner. The underlying conceptof the present invention is to have variations in the range of clearanceaccommodated primarily by the narrow sealing ribs 28 to avoid placingthe body 26 of the resilient ring under such high radial compression asto cause the ring to bind on the screw 24 of the actuator. Thus at themaximum clearance between the nut 22 and the screw 24 in the given rangeof clearances the two sealing ribs 28 are in effective pressure contactwith the inner surface of the inner channel 25 and, on the other hand,at the minimum clearance in the range of clearances the sealing ribs 28are compressed against the body 26 of the resilient ring withoutoverstressing the body'of the resilient ring.

In one embodiment of the invention, the radial dimension of the ribs 28at a point of minimum clearance between the nut 22 and the screw 24 isat least approximately one-half the maximum clearance in the range ofclearances. In another embodiment, the radial dimension of the ribs 28at the point of minimum clearance substantially exceeds one-half themaximum clearance in the range of clearances. These dimensionallimitations are preferred to prevent excessive stressing of the body ofthe ring 20 at the minimum clearance in the range of clearances.

FIG. 4 illustrates a second embodiment of the invention which differsfrom the first embodiment solely in the manner in which the resilientring 200 is interlocked with the surrounding nut 22a. The nut 220 hasthe usual inner circumferential channel 250 and has a radial bore 32a.Instead of being formed with a radial projection, the resilient ring 204is formed with a radial bore 44 that registers with the radial bore 32aof the nut and a suitable pin 45 seats in the two bores 32a and 44 tointerlock the resilient ring with the surrounding nut 22a. Here again,the radial bore 32a of the nut is sufficiently oversized relative to theradial pin 45 to permit the desired freedom for axial shift of thesealing ring in the inner channel 25a. It is apparent that the resilientring 20a functions in the same manner as the previously describedresilient ring 20 with the two outer circumferential sealing ribs 28 ofthe resilient ring compensating for most if not all of the clearanceswithin the given range of clearances between the nut and the screw.

FIG. 5 shows how the interlocking of a resilient ring 20b with asurrounding nut 22b may be accomplished by means of a key 46 that seatsboth in an inner keyway 48 of the nut and a cooperating outer keyway 50of the resilient ring. It can be seen that the key 46 is shorter thanthe outer keyway 48 to give the resilient ring 2017 the desired freedomfor axial shift in the inner channel 25b of the nut 22b.

It is apparent in FIG. 5 that the employment of the key 46 forinterlocking the resilient ring with the nut destroys the sealingeffectiveness of the outermost of the two outer circum ferential sealingribs 28b of the resilient ring but the innermost sealing rib is leftintact to function as an effective seal. Although the outermost sealingrib does not function as an effective seal, nevertheless it has utilityin cooperating with the innermost sealing rib for balanced pressurecontact with the inner surface of the channel 25b.

The embodiment shown in FIGS. 6 and 7 is largely similar to theembodiment shown in FIG. 5 as indicated by the use of correspondingnumerals to indicate corresponding parts. One difference is that the nut22c is not formed with an inner keyway and the other difference is thata short key 52 equipped with a radial pin 54 is substituted for the key46 in FIG. 7. The key 52 slidingly seats in an outer keyway 55 of thering 20c and the small radial pin fits snugly into a correspondingradial bore 56 of the nut 220. Since the key 52 is substantially shorterthan the keyway 55 of the ring 20c, the ring has ample freedom to shiftaxially to accommodate backlash between the screw and the nut.

In the embodiment of the invention shown in FIGS. 8-10, the sealing ring20d is seated in an inner channel 25dof a nut 22d and is formed with aradial projection 58 which extends into an oversized radial bore 60 ofthe nut. The resilient ring 20d has a single central outercircumferential sealing rib 62 that extends around all of itscircumference except in the region of the radial projection 58 where thesingle sealing ring 62 is continued as a circular sealing rib 64 thatsurrounds the radial projection 58. The diameter of the circular sealingrib 64 is sufficiently larger than the radial bore 60 of the nut 22d tokeep the circular sealing rib away from the radial bore at the extremepositions of the resilient ring 20d relative to the channel 25d to makesure that sealing effectiveness is maintained.

The embodiment of the invention shown in FIG. 11 is largely identical tothe embodiment shown in FIGS. 8-10 as indicated by the use ofcorresponding numerals to indicate corresponding parts. The soledifference is that the sealing ring e in FIG. 11 is interlocked with thenut 22c by a pin 65, the pin 65 slidingly seated in the radial bore 60of the nut He and snugly fitted into a radial bore 66 of the resilientring.

My description in specific detail will suggest various changes,substitutions and other departures from my disclosure within the spiritand scope of the appended claims.

I claim:

1. In a ball screw actuator having a screw embraced by a nut with givendimensional tolerances of the nut and screw providing a given range ofclearances between the nut and the screw, wherein the screw has anouter'circumferential helical groove cooperating with an innercircumferential helical groove of the nut to form a ball race,

the improvement to seal off the ball race from one end of the nut and tokeep lubricant in the ball race and to prevent foreign material fromentering the ball race, comprising:

the nut being formed with a continuous inner circum-- ferential channel;

a resiliently deformable elastomer ring seated in the channel; and

cooperative means on the nut and the ring respectively interlocking thenut and the ring to prevent rotation of the ring relative to the nut,

.said ring having a body with an outer circumferential surface and atleast two side surfaces defining the width of the ring, and having atleast one continuous sealing rib disposed on the outer circumferentialsurface of the body and of substantially less width than the width ofthe body for continuous sealing contact with the bottom wall of thechannel,

the radial dimension of the ring including the sealing rib relative tothe radial dimension of the channel being of a magnitude for the ring toform an effective seal between the nut and the screw without bindingcompression of the body of the ring at the minimum clearance in saidrange of clearances,

the radial dimension of the rib being of a magnitude for the ring toform an effective seal between the nut and screw at maximum clearancewithin said range,

whereby compensation for the range of clearances between the nut and thescrew is provided primarily by resilient compression of the sealing ribas distinguished from compression of the body of the ring.

2. An improvement as set forth in claim 1 in which the radial dimensionof the rib at a point of minimum clearance in the range of clearances isat least approximately one-half of the maximum clearance in said rangeof clearances to prevent excessive stressing of the body of the ring atthe minimum clearance in the range of clearances.

3. An improvement as set forth in claim 1 in which the radial dimensionof the sealing rib substantially exceeds one-half of the maximumclearance in said range of clearances to prevent excessive stressing ofthe body of the ring at the minimum clearance in the range ofclearances.

4. An improvement as set forth in claim 1 in which the innercircumference of the ring embraces at least one full turn of the helicalgroove of the screw.

5. An improvement as set forth in claim 1 in which the channel is widerthan the ring to provide the ring with freedom of axial movement withinat least a portion of the channel, and in which the interlocking meanspermits said freedom of axial movement to accommodate backlash betweenthe screw and the nut.

6. An improvement as set forth in claim 1 in which the ring is made ofpolyethylene.

7. An improvement as set forth in claim 1 in which the ring has a firstcontinuous outer circumferential sealing rib adjacent one of the sideedges of the ring and cooperating with the channel to maintain thelubricant upon the helical groove of the nut, and a second continuousouter circumferential sealing ring adjacent the other of the side edgesof the ring and cooperating with the channel to sealforeign matterexterior of the nut from the lubricant.

8. An improvement as set forth in claim 1 in which the ring has a singleouter circumferential sealing rib centrally disposed upon thecircumference of the ring except in the region of the interlockingmeans, the surrounding sealing rib being continuous with the singlesealing rib. v

9. An improvement as set forth in claim 1 in which the cooperatinginterlocking means comprises a recess in one of said nut and said ringand means projecting into the recess from the other of said nut and saidring, said projecting means being of less cross section than the recessto permit the ring to shift axially in the channel.

10. An improvement as set forth in claim 9 in which the recess is in thenut and the projecting means is integral with the ring.

11. An improvement as set forth in claim 9 in which the recess is in thering.

12. An improvement as set forth in claim 1 in which the nut has a radialbore in the region of the channel and means projects from the ring intothe bore to interlock the ring with the nut, the bore being oversizedrelative to the projecting means to permit the ring to shift axially inthe channel.

13. An improvement as set forth in claim 12 in which said projectingmeans is integral with the ring.

14. An improvement as set forth in claim 12 in which the ring has aradial bore registered with the radial bore of the nut,

and the projecting means comprises a pin which extends through the twobores to interlock the ring with the nut.

15. An improvement as set forth in claim 1 in which one of said nut andsaid ring has a keyway substantially parallel with its axis and keyanchored to the other of said nut and said ring slidingly engages saidkeyway to prevent rotation of the ring relative to the nut, the keybeing shorter than the keyway to permit the ring to shift axially withinthe channel.

16. An improvement as set forth in claim 15 in which the keyway is inthe outer circumference of the ring and the key is anchored to the nut.

17. In a ball screw actuator comprising a screw having an outercircumferential helical groove embraced by a nut having a helical grooveon the inner circumferential surface, a seal for wiping the helicalgroove of the screw and sealing a lubricant within the actuator,comprising:

a resiliently deformable ring having an inner surface for wiping thehelical groove of the screw and an outer circumferential surface forslidingly engaging at least a portion of the inner circumferentialsurface of the nut;

first means extending from the circumferential surface of the nut anddisposed relative to the ring and the nut and having a configurationrelative to the nut for resisting the rotation of the ring relative tothe nut while permitting the axial movement of the ring relative to thenut along at least a portion of the inner circumferential surface of thenut; and

second means extending from the circumferential surface of the ring andhaving a configuration relative to the nut to provide a seal between thering and the nut, the second means having properties for absorbingsubstantially all of the overstressing of the ring relative to the nutwhen the clearance between the screw and the nut is reduced whereby theconfiguration of the ring is substantially maintained.

18. A seal as set forth in claim 17 wherein the first means includes arecess in one of said nut and said ring and means projecting into therecess from the other of said nut and said ring, said projecting meansbeing of less axial cross section than the recess to permit the ring toshift axially on at least a portion of the inner circumferential surfaceof the nut.

19. A sea] as recited in claim 18 whereinthe recess is in the nut andthe projecting means is integral with the ring.

20. A seal as defined in claim 18 in which the recess is in the ring.

21. A seal as defined in claim 17 wherein the second means comprises:

at least one continuous annular lip integral with the ring fordisplacing the outer circumferential surface of the ring from the inner,circumferential surface of the nut, wherein an outward radial force onthe ring tends to flatten the lip to decrease the distance between thering and the inner circumferential surface of the nut so that theconfirmation of the ring is substantially maintained. 22. The seal asset forth in claim 17 wherein the ring has a body portion defined by:

a pair of axially displaced side surfaces and the inner and outercircumferential surfaces and; wherein the continuous annular lip isdisposed on the outer circumferential surface of the ring to space thering from the inner circumferential surface of the nut 23. The seal asrecited in claim 22 wherein the annular lip has an axial widthsubstantially less than the axial width of the ring between the pair ofside surfaces so that a radial force on the ring creates a greaterpressure on the annular lip than on the body portions of the ringwhereby the annular lip is substantially deformed and the confirmationof the body portion is substantially maintained.

It I! i i

1. In a ball screw actuator having a screw embraced by a nut with givendimensional tolerances of the nut and screw providing a given range ofclearances between the nut and the screw, wherein the screw has an outercircumferential helical groove cooperating with an inner circumferentialhelical groove of the nut to form a ball race, the improvement to sealoff the ball race from one end of the nut and to keep lubricant in theball race and to prevent foreign material from entering the ball race,comprising: the nut being formed with a continuous inner circumferentialchannel; a resiliently deformable elastomer ring seated in the channel;and cooperative means on the nut and the ring respectively interlockingthe nut and the ring to prevent rotation of the ring relative to thenut, said ring having a body with an outer circumferential surface andat least two side surfaces defining the width of the ring, and having atleast one continuous sealing rib disposed on the outer circumferentialsurface of the body and of substantially less width than the width ofthe body for continuous sealing contact with the bottom wall of thechannel, the radial dimension of the ring including the sealing ribrelative to the radial dimension of the channel being of a magnitude forthe ring to form an effective seal between the nut and the screw withoutbinding compression of the body of the ring at the minimum clearance insaid range of clearances, the radial dimension of the rib being of amagnitude for the ring to form an effective seal between the nut andscrew at maximum clearance within said range, whereby compensation forthe range of clearances between the nut and the screw is providedprimarily by resilient compression of the sealing rib as distinguishedfrom compression of the body of the ring.
 2. An improvement as set forthin claim 1 In which the radial dimension of the rib at a point ofminimum clearance in the range of clearances is at least approximatelyone-half of the maximum clearance in said range of clearances to preventexcessive stressing of the body of the ring at the minimum clearance inthe range of clearances.
 3. An improvement as set forth in claim 1 inwhich the radial dimension of the sealing rib substantially exceedsone-half of the maximum clearance in said range of clearances to preventexcessive stressing of the body of the ring at the minimum clearance inthe range of clearances.
 4. An improvement as set forth in claim 1 inwhich the inner circumference of the ring embraces at least one fullturn of the helical groove of the screw.
 5. An improvement as set forthin claim 1 in which the channel is wider than the ring to provide thering with freedom of axial movement within at least a portion of thechannel, and in which the interlocking means permits said freedom ofaxial movement to accommodate backlash between the screw and the nut. 6.An improvement as set forth in claim 1 in which the ring is made ofpolyethylene.
 7. An improvement as set forth in claim 1 in which thering has a first continuous outer circumferential sealing rib adjacentone of the side edges of the ring and cooperating with the channel tomaintain the lubricant upon the helical groove of the nut, and a secondcontinuous outer circumferential sealing ring adjacent the other of theside edges of the ring and cooperating with the channel to seal foreignmatter exterior of the nut from the lubricant.
 8. An improvement as setforth in claim 1 in which the ring has a single outer circumferentialsealing rib centrally disposed upon the circumference of the ring exceptin the region of the interlocking means, the surrounding sealing ribbeing continuous with the single sealing rib.
 9. An improvement as setforth in claim 1 in which the cooperating interlocking means comprises arecess in one of said nut and said ring and means projecting into therecess from the other of said nut and said ring, said projecting meansbeing of less cross section than the recess to permit the ring to shiftaxially in the channel.
 10. An improvement as set forth in claim 9 inwhich the recess is in the nut and the projecting means is integral withthe ring.
 11. An improvement as set forth in claim 9 in which the recessis in the ring.
 12. An improvement as set forth in claim 1 in which thenut has a radial bore in the region of the channel and means projectsfrom the ring into the bore to interlock the ring with the nut, the borebeing oversized relative to the projecting means to permit the ring toshift axially in the channel.
 13. An improvement as set forth in claim12 in which said projecting means is integral with the ring.
 14. Animprovement as set forth in claim 12 in which the ring has a radial boreregistered with the radial bore of the nut, and the projecting meanscomprises a pin which extends through the two bores to interlock thering with the nut.
 15. An improvement as set forth in claim 1 in whichone of said nut and said ring has a keyway substantially parallel withits axis and key anchored to the other of said nut and said ringslidingly engages said keyway to prevent rotation of the ring relativeto the nut, the key being shorter than the keyway to permit the ring toshift axially within the channel.
 16. An improvement as set forth inclaim 15 in which the keyway is in the outer circumference of the ringand the key is anchored to the nut.
 17. In a ball screw actuatorcomprising a screw having an outer circumferential helical grooveembraced by a nut having a helical groove on the inner circumferentialsurface, a seal for wiping the helical groove of the screw and sealing alubricant within the actuator, comprising: a resiliently deformable ringhaving an inner surface for wiping the helical groove of the screw andan outer circumferential surface for slidingly engaGing at least aportion of the inner circumferential surface of the nut; first meansextending from the circumferential surface of the nut and disposedrelative to the ring and the nut and having a configuration relative tothe nut for resisting the rotation of the ring relative to the nut whilepermitting the axial movement of the ring relative to the nut along atleast a portion of the inner circumferential surface of the nut; andsecond means extending from the circumferential surface of the ring andhaving a configuration relative to the nut to provide a seal between thering and the nut, the second means having properties for absorbingsubstantially all of the overstressing of the ring relative to the nutwhen the clearance between the screw and the nut is reduced whereby theconfiguration of the ring is substantially maintained.
 18. A seal as setforth in claim 17 wherein the first means includes a recess in one ofsaid nut and said ring and means projecting into the recess from theother of said nut and said ring, said projecting means being of lessaxial cross section than the recess to permit the ring to shift axiallyon at least a portion of the inner circumferential surface of the nut.19. A seal as recited in claim 18 wherein the recess is in the nut andthe projecting means is integral with the ring.
 20. A seal as defined inclaim 18 in which the recess is in the ring.
 21. A seal as defined inclaim 17 wherein the second means comprises: at least one continuousannular lip integral with the ring for displacing the outercircumferential surface of the ring from the inner circumferentialsurface of the nut, wherein an outward radial force on the ring tends toflatten the lip to decrease the distance between the ring and the innercircumferential surface of the nut so that the confirmation of the ringis substantially maintained.
 22. The seal as set forth in claim 17wherein the ring has a body portion defined by: a pair of axiallydisplaced side surfaces and the inner and outer circumferential surfacesand; wherein the continuous annular lip is disposed on the outercircumferential surface of the ring to space the ring from the innercircumferential surface of the nut.
 23. The seal as recited in claim 22wherein the annular lip has an axial width substantially less than theaxial width of the ring between the pair of side surfaces so that aradial force on the ring creates a greater pressure on the annular lipthan on the body portions of the ring whereby the annular lip issubstantially deformed and the confirmation of the body portion issubstantially maintained.